Engine braking is commonly used in heavy goods vehicles in which the engine is temporarily converted into an energy absorber while being motored by the vehicle and the fuel to the engine is shut off. To increase the braking torque generated by this motored engine, an engine braking device, which is a temporarily operated valve actuating mechanism, is commonly installed in the engine for modifying the valve timing of the engine to allow the compression pressure, generated within the engine cylinder during the compression stroke of the engine, to be released irreversibly from the engine. Traditionally, the exhaust valve of the engine is kept opened during the compression stroke of the engine when the engine braking device is activated and the energy of the compressed air is released to the exhaust system of the engine. Similarly, the intake valve of the engine may be kept open during the compression stroke of the engine producing a similar engine braking effect but the energy of the compressed air is released to the intake system of the engine.
In either case, instead of wasting this compressed air energy generated during braking, it has been proposed to divert it to a compressed air storage tank so that it can be captured and re-used for various purposes in the vehicle after braking. This represents an air hybrid vehicle in which the engine is selectively operable is several modes, namely, normal fuel burning mode producing power for driving of the vehicle, air compressor mode absorbing power and producing compressed air during braking of the vehicle, and possibly, air motor mode re-using the captured compressed air to drive the engine.
In the above air hybrid vehicle when the engine is operating in the air compressor mode, the engine braking device acting on either the exhaust valve or the intake valve of the engine is activated to achieve compression release from the engine cylinder. At the same time, an air diverting device is required to capture the compressed air from the exhaust system or intake system of the engine, respectively. Such an air diverting device will have a similar function and design when installed in either location but the operating environment will have to be taken into account in view of the higher temperature of the exhaust system. In this context, it is preferred to transfer the installation of the engine braking device from its traditional position acting on the exhaust valve to a similar position acting on the intake valve producing similar engine braking effect, thus allowing the air diverting device to be installed in the intake system of the engine which will be more economical and durable.